This invention relates to sulfur dioxide removal from fluidized-bed combustion processes. It is of particular interest in respect to the fluidized-bed combustion of coal, but processes for the combustion of other sulfur-containing materials such as coke, char, wood and combustible waste from industrial, commercial or residential sources might also incorporate the present method.
Previous methods for removing sulfur dioxide from conventional boilers have included fixed-bed reactors through which effluent gases are passed. Such reactors have included a wide range of metal oxides supported on such as alumina substrates. However, in a high-temperature, fluidized-bed combustion unit, these methods are of limited utility as it is desirable to pass the high-temperature gas directly to a gas turbine or other device for the generation of electricity. Therefore, materials such as limestone or dolomite have been fluidized with the coal or other fossil fuel to react with sulfur dioxide and form sulfates. The sulfated limestone or dolomite is then removed from the combustion process and regenerated by fluidization within a reducing gas such as hydrogen, carbon monoxide or methane. Unfortunately, only a portion of the dolomite or limestone sulfates and then only a portion of that sulfated is regenerated to the oxide. Consequently, the reactivity of these materials decreases with each sulfation-regeneration cycle. Also, severe decrepitation of the limestone or dolomite particles occurs during regeneration to produce fines that are not easily retained within the fluidized-bed combustion process.
Therefore, in view of these disadvantages of the prior art, it is an object of the present invention to provide an improved method for removing sulfur dioxide emissions produced in a fluidized-bed combustion process.
It is a further object to provide such a method of sulfur dioxide removal in which materials sulfated within the fluidized bed can be regenerated with reduced decrepitation.
It is a further object to provide a method of preparing particles of support material impregnated with a metal oxide for removal of sulfur dioxides within a fluidized-bed combustion process.